Valve system for a coulometric analyte sensing instrument

ABSTRACT

A valve system that includes (i) first and second longitudinally facing members defining a gap therebetween in fluid communication with transversely offset first and second orifices through the members, (ii) a primary biasing means longitudinally biasing the members away from one another, (iii) an elastic element positioned within the gap between the first and second orifices, and (iv) a repositioning means for longitudinally repositioning one of the members towards the other member against the bias of the primary biasing means for adjusting the longitudinal height of the gap. The members can be repositioned between (a) a first position wherein the elastic element does not seal the gap so as to allow fluid flow from the first orifice to the second orifice through the gap, and (b) a second position wherein the elastic element is compressed between the members and seals the gap so as to prevent fluid flow from the first orifice to the second orifice through the gap.

BACKGROUND

Permeation instruments are used to measure the transmission rate of atarget analyte, such as oxygen, carbon dioxide or water vapor, through afilm of interest. Typical films subjected to permeation testing arepolymeric packaging films such as those constructed from low densitypolyethylene (LDPE), high density polyethylene (HDPE), orientedpolypropylene (OPP), polyethylene terepthalate (PET), polyvinylidenechrloride (PVTDC), etc. Typically, the film to be tested is positionedwithin a test chamber to sealing separate the chamber into first andsecond cells. The first cell (commonly referenced as the sensing cell)is flushed with an inert gas to remove any target analyte from the celland the second cell (commonly referenced as the analyte cell) filledwith a gas containing a known concentration of the target analyte. Asensor for the target analyte detects the presence of target analytethat has migrated into the sensing cell from the analyte cell throughthe film.

Permeation instruments typically employ a flow-through method or anaccumulation method for sensing the presence of target analyte in thesensing cell. Briefly, the flow-through method uses an inert flushinggas to continuously pick up any target analyte that has migrated intothe sensing cell and deliver it to a remote sensor. The accumulationmethod allows target analyte to build up in the sensing cell for anaccumulation period, with the sensor either positioned within thesensing cell or the sensing cell flushed with a flushing gas after theaccumulation period for delivery of accumulated target analyte to aremote sensor.

Both methods require precision in timing the opening and closing offluid flows through the instrument, as well as opening and closingaccess to the analyte sensor. In addition, when sensing cell is sealedto fluid flow during a testing period, such as occurs with theaccumulation technique, the instrument is relying solely upon diffusionto move analyte molecules within the sensing cell into sensing contactwith the sensor, and the valving system should not seal the sensing celltoo far upstream or downstream from the cell as this causes an increasein the effective volume of the sensing cell, thereby reducing theresponsiveness and accuracy of the instrument.

Accordingly, a substantial need exists for a valving system forpermeation testing instruments capable of reliably and consistentlyopening and closing the various cells within the instrument to fluidflow with a limited increase in the effective volume of the sensing cellof the instrument.

SUMMARY OF THE INVENTION

The invention is directed to a valve system. One embodiment of the valvesystem includes (i) first and second longitudinally facing membersdefining a gap therebetween in fluid communication with transverselyoffset first and second orifices through the members, (ii) a primarybiasing means longitudinally biasing the members away from one another,(iii) an elastic element positioned within the gap between the first andsecond orifices, and (iv) a repositioning means for longitudinallyrepositioning one of the members towards the other member against thebias of the primary biasing means for adjusting the longitudinal heightof the gap. The members can be repositioned between (a) a first positionwherein the elastic element does not seal the gap so as to allow fluidflow from the first orifice to the second orifice through the gap, and(b) a second position wherein the elastic element is compressed betweenthe members and seals the gap so as to prevent fluid flow from the firstorifice to the second orifice through the gap.

Another embodiment of the valve system includes (i) first and secondlongitudinally facing members defining a gap therebetween in fluidcommunication with a first inlet and a first outlet orifice through onemember and a second inlet and a second outlet orifice through the othermember, wherein (a) the inlet orifices are transversely offset, (b) theoutlet orifices are transversely offset, and (c) one of the members islongitudinally repositionable relative to the other member for adjustingthe longitudinal height of the gap, (ii) an inlet larger-diameterelastic O-ring positioned within the gap and encompassing both the firstand second inlet orifices, (iii) an inlet smaller-diameter elasticO-ring positioned within the gap and surrounding only one of the firstor second inlet orifices, (iv) an outlet larger-diameter elastic O-ringpositioned within the gap and encompassing both the first and secondoutlet orifices, (v) an outlet smaller-diameter elastic O-ringpositioned within the gap and surrounding only one of the first orsecond outlet orifices, and (vi) a repositioning means forlongitudinally repositioning the repositionable member towards the othermember against the bias of the larger-diameter elastic O-rings. Themembers can be repositioned between (a) a first position wherein thelarger-diameter O-rings are compressed between the members and seal thegap so as to prevent fluid flow through the gap from the inlet orificesto the outlet orifices without compressing the smaller-diameter O-ringsbetween the members so as to allow fluid flow from the first inletorifice to the second inlet orifice through the gap and from the firstoutlet orifice to the second outlet orifice through the gap, and (b) asecond position wherein both larger-diameter O-rings are compressedbetween the members and seal the gap so as to prevent fluid flow throughthe gap from the inlet orifices to the outlet orifices, the inletsmaller-diameter O-ring is compressed between the members so as toprevent fluid flow from the first inlet orifice to the second inletorifice through the gap, and the inlet smaller-diameter O-ring iscompressed between the members so as to prevent fluid flow from thefirst outlet orifice to the second outlet orifice through the gap.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic overview of one embodiment of a testing systemuseful for performing the testing process of the present invention.

FIG. 2 is a side view of the measurement unit component of the testingsystem shown in FIG. 1.

FIG. 3 is a top view of the measurement unit component of the testingsystem shown in FIG. 2.

FIG. 4A is a cross-sectional side view of the measurement unit shown inFIG. 3 taken along line 4-4 with the upper mounting plate in the openposition spaced a distance away from the upper portion of the housing.

FIG. 4A ¹ is an enlarged cross-sectional side view of the encircledinlet area of the gap in the measurement unit shown in FIG. 4A.

FIG. 4A ² is an enlarged cross-sectional side view of the encircledoutlet area of the gap in the measurement unit shown in FIG. 4A.

FIG. 4A ³ is an enlarged cross-sectional side view of the encircledsensor passageway area of the gap in the measurement unit shown in FIG.4A.

FIG. 4B is a cross-sectional side view of the measurement unit shown inFIG. 3 taken along line 4-4 with the upper mounting plate in the closedposition immediately adjacent the upper portion of the housing.

FIG. 4B ¹ is an enlarged cross-sectional side view of the encircledinlet area of the gap in the measurement unit shown in FIG. 4B.

FIG. 4B ² is an enlarged cross-sectional side view of the encircledoutlet area of the gap in the measurement unit shown in FIG. 4B.

FIG. 4B ³ is an enlarged cross-sectional side view of the encircledsensor passageway area of the gap in the measurement unit shown in FIG.4B.

FIG. 5A is a cross-sectional side view of the measurement unit shown inFIG. 3 taken along line 5-5 with the upper mounting plate in the openposition spaced a distance away from the upper portion of the housing.

FIG. 5A ¹ is an enlarged cross-sectional side view of the encircledhumidity control window in the measurement unit shown in FIG. 5A.

FIG. 5B is a cross-sectional side view of the measurement unit shown inFIG. 3 taken along line 5-5 with the upper mounting plate in the closedposition immediately adjacent the upper portion of the housing.

FIG. 5B ¹ is an enlarged cross-sectional side view of the encircledhumidity control window in the measurement unit shown in FIG. 5B.

FIG. 6A is a cross-sectional side view of the measurement unit shown inFIG. 3 taken along line 6-6 with the upper mounting plate in the openposition spaced a distance away from the upper portion of the housing.

FIG. 6B is a cross-sectional side view of the measurement unit shown inFIG. 3 taken along line 6-6 with the upper mounting plate in the closedposition spaced a distance away from the upper portion of the housing.

FIG. 7 is a grossly enlarged side view of the encircled portion of thetesting chamber shown in FIG. 3 depicting individual molecules of ananalyte of interest on each side of a test film being tested with themeasurement unit shown in FIG. 4B.

FIG. 8 is a graph of the O₂ transmission rate over time obtained fromthe permeation testing conducted in Example 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Nomenclature

-   10 Testing System-   21 Source of Inert Gas-   22 Source of Test Gas-   31 a Inlet Shutoff Valve for Source of Inert Gas-   31 b Outlet Shutoff Valve for Source of Inert Gas-   32 a Inlet Shutoff Valve for Source of Test Gas-   32 b Outlet Shutoff Valve for Source of Test Gas-   41 a Inlet Conduit for Directing Gas From the Source of Inert Gas    Into the Upper Cell-   41 b Outlet Conduit for Venting Gas From the Upper Cell-   42 a Inlet Conduit for Directing Gas From the Source of Test Gas    Into the Lower Cell-   42 b Outlet Conduit for Venting Gas From the Lower Cell-   50 Computer or CPU-   60 Monitor-   70 Printer-   80 Electrical Leads from the Sensor to the CPU-   100 Measurement Unit-   110 Housing-   111 Upper Section of Housing-   111 i Lower Surface of Upper Section of Housing-   112 Lower Section of Housing-   119 Retention Chamber Defined by Housing-   120 Mounting Plates-   121 Upper Mounting Plate-   121 u Upper Surface of Upper Mounting Plate-   121 n Pin On Upper Mounting Plate-   122 Lower Mounting Plate-   125 O-ring Between Mounting Plates-   129 Testing Chamber Defined by Mounting Plates-   129 ¹ Upper Cell of Testing Chamber-   129 ² Lower Cell of Testing Chamber-   130 Actuator-   131 Actuator Shaft-   140 Valve for Passageway to Analyte Sensor-   141 Valve Body-   142 Valve Stem-   151 a Inlet Channel to Lower Cell Through Upper Section of Housing-   151 b Inlet Channel to Lower Cell Through Upper Mounting Plate-   151 c Inlet Channel to Lower Cell Through Lower Mounting Plate-   151 w Larger O-ring within Gap Encircling Inlet Passageways into the    Lower Cell-   152 a Outlet Channel from Lower Cell Through Upper Section of    Housing-   152 b Outlet Channel from Lower Cell Through Upper Mounting Plate-   152 c Outlet Channel from Lower Cell Through Lower Mounting Plate-   152 w Larger O-ring within Gap Encircling Outlet Passageways from    the Lower Cell-   160 Gap Between Upper Section of Housing and Upper Mounting Plate-   170 Flow Control Channels and Passageways Through the Upper Section    of the Housing and the Upper Mounting Plate-   171 a Inlet Channel to Gap Through Upper Section of Housing-   171 b Inlet Channel from Gap to Upper Cell Through Upper Mounting    Plate-   172 a Outlet Channel from Gap Through Upper Section of Housing-   172 b Outlet Channel from Upper Cell to Gap Through Upper Mounting    Plate-   173 a Passageway from Gap to Analyte Sensor Through Upper Section of    Housing-   173 b Passageway from Upper Cell to Gap Through Upper Mounting Plate-   180 O-Ring Seals within the Gap-   181 v Smaller O-ring within Gap Encircling Inlet Channel through    Upper Mounting Plate-   181 w Larger O-ring within Gap Encircling Both Inlet Channels-   182 v Smaller O-ring within Gap Encircling Outlet Channel through    Upper Mounting Plate-   182 w Larger O-ring within Gap Encircling Both Outlet Channels-   183 w Larger O-ring within Gap Encircling Passageways Leading to the    Sensor-   190 Humidity Control System-   191 a Inlet Channel to Humidity Control Chamber Through Upper    Section of Housing-   192 a Outlet Channel from Humidity Control Chamber Through Upper    Section of Housing-   193 Selectively Permeable Film-   194 O-ring-   195 Washer-   196 Inset Ring-   197 Locking Ring-   198 w Larger O-ring within Gap Encircling Both Inlet and Outlet    Channels for a Humidity Control Chamber-   199 Humidity Control Chambers in the Upper Mounting Plate-   200 Analyte Sensor-   A Analyte Molecules-   F Film Being Tested-   x Lateral Direction-   y Longitudinal Direction-   z Transverse Direction

DESCRIPTION

Overview

Referring generally to FIG. 1, the invention is directed to a valvesystem for an analyte measurement unit 10. The valve system ensures thatthe flow of various fluids through the unit 10 occur in the properlysequence as necessary and appropriate for measuring the effective volumeof the sensing cell 129 ¹ of the measurement unit 10.

The method includes the steps of (i) separating a testing chamber 129into a first or upper cell 129 ¹ and a second or lower cell 129 ² with aknown area of a film F, (ii) flushing the first cell 129 ¹ with an inertgas to remove any target analyte A from the first cell 129 ¹, (iii)introducing a gas (not shown) containing a known concentration of ananalyte A into the lower cell 129 ², (iv) sealing the upper cell 129 ¹to gas flow (not shown) through the upper cell 129 ¹, and (v) sensingany analyte A in the upper cell 129 ¹ with an analyte sensor 200 thatconsumes the analyte A at a rate greater than the rate at which theanalyte A is passing through the film F, until a steady state rate ofanalyte A consumption is measured by the analyte sensor 200. The analytesensor 200 preferably consumes analyte A at least ten times faster thanthe rate at which the analyte A is transmitted through the film F, morepreferably twenty times faster, and most preferably one hundred timesfaster.

Referring to FIGS. 4A and 4B, the valve system includes (i) an uppersection 111 of a housing 110 and an upper mounting plate 121 defining agap 160 therebetween, (ii) a means for reposition the mounting plate 121relative to the upper section 111 of the housing 110 as between an openposition with a “thicker” gap 160 and a closed position with a “thinner”gap 160, (iii) flow control channels and passageways 170 through theupper section 111 of the housing 110 and the upper mounting plate 121and (iv) o-ring seals 180 of different diameters and differentthicknesses positioned within a gap 160, encircling the various channelsand passageways 170.

Referring to FIGS. 4A and 4A ¹, fluid flow into the upper cell 129 ¹ isprovided by laterally x and/or transversely z offset inlet channels 171a and 171 b in the upper section 111 of the housing 110 and the uppermounting plate 121 respectively. In similar fashion, referring now toFIGS. 4A and 4A ², fluid flow out from the upper cell 129 ¹ is providedby laterally x and/or transversely z offset outlet channels 172 a and172 b in the upper section 111 of the housing 110 and the upper mountingplate 121 respectively.

Referring to FIGS. 4A and 4A ¹, a small diameter o-ring 181 v ispositioned within the gap 160 encircling just one of the inlet channels171 b, while a large diameter o-ring 181 w, also positioned within thegap 160, encircles both inlet channels 171 a and 171 b. In similarfashion, referring now to FIGS. 4A and 4A ², a small diameter o-ring 182v is positioned within the gap 160 encircling just one of the outletchannels 172 b, while a large diameter o-ring 182 w, also positionedwithin the gap 160, encircles both the outlet channels 172 a and 172 b.

Referring to FIGS. 4A, 4A¹, 4A², 4A³, 5A, 5A¹, the thickness orlongitudinal y height of the o-rings 181 and 182 are selected so thatthe large diameter o-rings 181 w and 182 w are sealingly engaged withinthe gap 160 regardless of whether the gap 160 is thicker or thinner,while the smaller diameter o-rings 181 v and 182 v are sealingly engagedwithin the gap 160 only when the gap is thinner. Such positioning of thelarger (181 w and 182 w) and smaller (181 v and 182 v) o-rings, incombination with the different thicknesses of the larger (181 w and 182w) and smaller (181 v and 182 v) o-rings, permits the inlet (171 a and171 b) and outlet (172 a and 172 b) channels to be simultaneously openedto fluid flow for flushing of the upper cell 129 ¹ prior to a testingperiod by longitudinally y moving the mounting plates 120 into thedownward or open position as shown in FIGS. 4A, 4A¹ and 4A², andsimultaneously closed to fluid flow for sealing-off the upper cell 129 ¹during a testing period by longitudinally y moving the mounting plates120 into the upward or closed position as shown in FIGS. 4B, 4B¹ and4B².

The film F can be a perforated or nonperforated film F, and can beporous or nonporous with respect to the target analyte A, so long as theanalyte sensor 200 can consume the target analyte A at a rate greaterthan the rate at which the analyte A is passing through the film F. Toensure that the analyte sensor 200 is consuming all target analyte Athat is passing through the film F, the analyte sensor 200 is preferablyselected so that it consumes target analyte A at a rate that is at leastten times greater, preferably twenty times greater and most preferably100 times greater, than the rate at which the target analyte A is likelyto be transmitted through the film F.

Specific Embodiment

Testing System

Construction

An exemplary embodiment of a testing system 10 capable of measuring thetransmission rate of an analyte A through a film F in accordance withthe present invention is depicted in FIG. 1. A measurement unit 100defines a testing chamber 129 sealingly divided by a film F to be testedinto an upper cell 129 ¹ and a lower cell 129 ². A source of an inertgas 21 communicates with the upper cell 129 ¹ via inlet conduit 41 a andoutlet conduit 41 b for flushing the upper cell 129 ¹ prior to testing.Suitable inert gases include specifically, but not exclusively,nitrogen, argon, helium, krypton or a blend of nitrogen and hydrogen,etc. A source of test gas 22 containing a known concentration of ananalyte A, communicates with the lower cell 129 ² via inlet conduit 42 aand outlet conduit 42 b for continuously providing the lower cell 129 ²with test gas to ensure that the concentration of analyte A within thelower cell 129 ² remains constant throughout a test period. Shutoffvalves 31 a and 31 b are provided in inlet conduit 41 a and outletconduit 41 b respectively, for controlling the flow of inert gas throughthe upper cell 129 ¹. Similarly, shutoff valves 32 a and 32 b areprovided in inlet conduit 42 a and outlet conduit 42 b respectively, forcontrolling the flow of gas through the lower cell 129 ².

An analyte sensor 200 for the target analyte A is placed in fluidcommunication with the upper cell 129 ¹ for sensing the presence oftarget analyte A within the upper cell 129 ¹. Typical target analytesinclude oxygen, carbon dioxide, carbon monoxide and water vapor. Theanalyte sensor 200 may be selected from any of the wide variety ofcommercially available consuming sensors capable of detecting andconsuming the target analyte A, with electrochemical sensors generallypreferred based upon the high sensitivity and low cost of such sensorsand the fact that such sensors, when employed in the present invention,follow Faraday's Law—eliminating the need to calibrate the sensor.

The analyte sensor 200 communicates via electrical leads 80 with asuitable central processing unit 50 equipped with electronic memory (notshown), and optionally but preferably attached to a monitor 60 and/orprinter 70 for storing and reporting analyte A concentrations detectedby the analyte sensor 200.

Use

A film F to be tested is “loaded” into the testing chamber 129 so as tosealingly separate the testing chamber 129 into an upper cell 129 ¹ anda lower cell 129 ² with a known area of the film F exposed to both cells129 ¹ and 129 ². Shutoff valves 31 a and 31 b are then opened to permitthe flow of inert gas through the upper cell 129 ¹ for flushing analyteA from the upper cell 129 ¹. After flushing, the shutoff valves 31 a and31 b are closed to seal-off the upper cell 129 ¹ from the surroundingenvironment. Shutoff valves 32 a and 32 b are then opened to permit theflow of gas containing a known concentration of analyte A into the lowercell 129 ². The presence of analyte A within the upper cell 129 ¹ isthen detected and recorded by the analyte sensor 200. By ensuring thatthe only route through which analyte A can enter into the upper cell 129¹ is through the “exposed” area of the film F, and by selecting ananalyte sensor 200 that consumes analyte A faster than the analyte A istransmitted through the film F, then the rate at which the analytesensor 200 detects analyte A, once a steady state rate is attained, canbe equated directly to the analyte transmission rate for the known“exposed” area of the film F.

Measurement Unit Including Valve System

Construction

An exemplary embodiment of a measurement unit 100 capable of quickly andaccurately measuring the transmission rate of an analyte A through afilm F in accordance with the present invention is depicted in FIGS.2-6.

The measurement unit 100 includes (i) a housing 110, (ii) mountingplates 120, (iii) an actuator 130, (iv) a valve 140 for controllingfluid communication with an analyte sensor 200, (v) channels 151 a, 151b, 151 c, 152 a, 152 b, and 152 c in the housing 110 and mounting plates120 for directing test gas (not shown) into a lower cell 129 ² in themounting plates 120, and (vi) a flow control system (not collectivelynumbered) including flow control channels 170 and o-ring seals 180 forselectively opening and sealing closing an upper cell 129 ¹ in themounting plates 120 to fluid flow. The measurement unit 100 optionally,but preferably, also includes a humidity control system 190.

The housing 110 includes an upper section 111 and a lower section 112that cooperatively define a retention chamber 119.

Referring to FIGS. 4A, 4B, 5A, 5B, 6A and 6B, upper and lower mountingplates 121 and 122 (collectively referenced as mounting plates 120) areretained within the retention chamber 119 defined by housing 110 withthe upper surface 121 u of the upper mounting plate 121 longitudinally yoffset a distance from the lower surface 111 i of the upper section 111of the housing 110 so as to define a gap 160 therebetween. The upper andlower mounting plates 121 and 122 define a testing chamber 129therebetween. An o-ring 125 encircling the testing chamber 129 isprovided between the mounting plates 120. The testing chamber 129 can besealingly divided into an upper cell 129 ¹ and a lower cell 129 ² byplacement of a test film F between the mounting plates 120 overlayingthe o-ring 125, and compressing the mounting plates 120 together so asto sealingly compress the entire periphery of the o-ring 125 between themounting plates 120.

It is generally preferred to configure the testing chamber 129 toprovide an upper cell 129 ¹ of about 1 cm³ to about 3 cm³. An upper cell129 ¹ larger than about 3 cm³ is too slow to respond as molecules ofanalyte A within the upper cell 129 ¹ can be consumed and detected bythe analyte sensor 200 only when the molecules enter the analyte sensor200 and the upper cell 129 ¹ relies solely upon diffusion to movemolecules within the upper cell 129 ¹. An upper cell 129 ¹ smaller thanabout 1 cm³ tends to cause areas of the film F to contact with the uppersurface (not numbered) of the upper mounting plate 121 during thetesting period, thereby introducing error into the test results asanalyte A cannot readily pass through the film F into the upper cell 129¹ through these “covered” areas.

Referring to FIGS. 4A, 4B, 5A, 5B, 6A and 6B, the lower mounting plate122 is mounted onto the distal end (unnumbered) of an actuator shaft 131for longitudinally repositioning of the mounting plates 120 by anactuator 130 as between a lower or open position creating alongitudinally thicker gap 160 between the upper surface 121 u of theupper mounting plate 121 and the lower surface 111 i of the uppersection 111 of the housing 110, as shown in FIG. 4 (collectively 4A,4A¹, 4A² and 4A³), and an upper or closed position creating alongitudinally thinner gap 160 between the upper surface 121 u of theupper mounting plate 121 and the lower surface 111 i of the uppersection 111 of the housing 110, as shown in FIG. 5 (collectively 5A,5A¹, 5A² and 5A³). Suitable actuators 130 include specifically, but notexclusively, pneumatic and hydraulic pistons.

Referring to FIGS. 6A and 6B, fluid flow into the lower cell 129 ² isprovided by aligned inlet channels 151 a, 151 b and 151 c in the uppersection 111 of the housing 110, the upper mounting plate 121 and thelower mounting plate 122 respectively. In similar fashion, fluid flowout from the lower cell 129 ² is provided by aligned outlet channels 152a, 152 b and 152 c in the upper section 111 of the housing 110, theupper mounting plate 121 and the lower mounting plate 122 respectively.A large diameter o-ring 151 w is positioned within the gap 160encircling the inlet channels 151 a and 151 b in the upper section 111of the housing 110 and the upper mounting plate 121 for preventingtesting gas from flowing throughout the gap 160. In similar fashion, alarge diameter o-ring 152 w is positioned within the gap 160 encirclingthe outlet channels 152 a and 152 b in the upper section 111 of thehousing 110 and the upper mounting plate 121 for preventing testing gasfrom flowing throughout the gap 160.

Referring to FIGS. 4A and 4B, the flow control system (not collectivelynumbered) includes (i) flow control channels and passageways 170 throughthe upper section 111 of the housing 110 and the upper mounting plate121, and (ii) o-ring seals 180 of different diameters and differentthicknesses positioned within the gap 160 and encircling the variouschannels and passageways 170. The flow control system provides a quick,simple and reliable method of opening and closing the upper cell 129 ¹and the analyte sensor 200 to fluid flow at the appropriate times.

Referring to FIGS. 4A and 4A ¹, fluid flow into the upper cell 129 ¹ isprovided by laterally x and/or transversely z offset inlet channels 171a and 171 b in the upper section 111 of the housing 110 and the uppermounting plate 121 respectively. In similar fashion, referring now toFIGS. 4A and 4A ², fluid flow out from the upper cell 129 ¹ is providedby laterally x and/or transversely z offset outlet channels 172 a and172 b in the upper section 111 of the housing 110 and the upper mountingplate 121 respectively.

Referring to FIGS. 4A and 4A ¹, a small diameter o-ring 181 v ispositioned within the gap 160 encircling the inlet channel 171 b in theupper mounting plate 121. A large diameter o-ring 181 w is alsopositioned within the gap 160 for encircling both the inlet channel 171a in the upper section 111 of the housing 110 and the inlet channel 171b in the upper mounting plate 121 as well as fully encircling the smalldiameter o-ring 181 v. In similar fashion, referring now to FIGS. 4A and4A ², a small diameter o-ring 182 v is positioned within the gap 160encircling the outlet channel 172 b in the upper mounting plate 121,with a large diameter o-ring 182 w positioned within the gap 160 andencircling both the outlet channel 172 a in the upper section 111 of thehousing 110 and the outlet channel 172 b in the upper mounting plate 121as well as encircling the small diameter o-ring 182 v.

Referring to FIGS. 4A, 4A¹, 4A², 4A³, 5A, 5A¹, the thickness orlongitudinal y height of the large diameter o-rings 181 w and 182 w isselected so that these o-rings 181 w and 182 w are sealingly engagedwithin the gap 160 regardless of whether the mounting plates 120 are inthe open or closed longitudinally y position so as to prevent fluid fromflowing freely within the gap 160. The thickness or longitudinal yheight of the smaller diameter o-rings 181 v and 182 v is selected sothat these o-rings 181 v and 182 v are sealingly engaged within the gap160 only when the mounting plates 120 are in the closed longitudinally yposition. Such positioning of the larger (181 w and 182 w) and smaller(181 v and 182 v) o-rings, in combination with the different thicknessesof the larger (181 w and 182 w) and smaller (181 v and 182 v) o-rings,permits the inlet (171 a and 171 b) and outlet (172 a and 172 b)channels to be simultaneously opened to fluid flow for flushing of theupper cell 129 ¹ prior to a testing period by longitudinally y movingthe mounting plates 120 into the downward or open position as shown inFIGS. 4A, 4A¹ and 4A², and simultaneously closed to fluid flow forsealing-off the upper cell 129 ¹ during a testing period bylongitudinally y moving the mounting plates 120 into the upward orclosed position as shown in FIGS. 4B, 4B¹ and 4B².

Referring to FIGS. 4A, 4A³, 5A, the analyte sensor 200 communicates withthe upper cell 129 ¹ via longitudinally y aligned passageways 173 a and173 b in the upper section 111 of the housing 110 and the upper mountingplate 121 respectively. A large diameter o-ring 183 w is positionedwithin the gap 160 encircling both passageways 173 a and 173 b forensuring that fluid diffusing into the analyte sensor 200 from the uppercell 129 ¹ is not contaminated by fluid from the gap 160.

In order to extend the useful life of the analyte sensor 200, especiallywhen an electrochemical sensor is employed, the passageway 173 a shouldbe closed at all times except during testing periods (i.e., only afterthe upper cell 129 ¹ has been flushed with an inert gas and sealed sothat the only analyte A in the upper cell 129 ¹ is analyte A that haspermeated through a test film F). Referring to FIGS. 4A, 4A³, 5A, anexpedient technique for providing such limited access to the analytesensor 200 is to position a normally closed tire valve 140 within thepassageway 173 a, with the body 141 of the tire valve 140 sealinglywedged into the passageway 173 a and the stem 142 of the tire valve 140extending longitudinally y downward towards the gap 160. An upwardlyextending pin 121 n is provided on the upper mounting plate 121 forpressing longitudinally y upward against the valve stem 142 and therebyopening the valve 140 only when the mounting plates 120 are in the upperor closed position.

The transmission rate of analyte A through most plastic films F issensitive to humidity, with an increase in humidity tending to result inan increase in the transmission rate. Most analyte sensors 200 are alsosomewhat sensitive to humidity, especially if permitted to “dry out”.Hence, in order to obtain consistent and comparable test results it isimportant to maintain a constant relative humidity within the testingchamber 129, especially within the closed upper cell 129 ¹. To maintaina constant humidity within the upper cell 129 ¹, a humidity controlsystem 190 can be provided. A suitable humidity control system 190 isshown in FIGS. 5A, 5A¹, 5B and 5B¹. The humidity control system 190include a pair of humidity control chambers 199 in the upper mountingplate 121 diametrically positioned relative to the analyte sensor 200and in fluid communication with both the upper cell 129 ¹ and the gap160. Inlet 191 a and outlet 192 a channels are provided in the uppersection 111 of the housing 110 for placing each of the humidity controlchambers 199 in fluid communication with a source of a gas (not shown)having a known humidity, typically 0% or 100% relative humidity. A largediameter o-ring 198 w is positioned within the gap 160 encircling eachof the humidity control chambers 199 and the corresponding set of inlet191 a and outlet 192 a channels. A film 193 permeable to water vapor andimpermeable to the target analyte A, such as a Nafion® film, is providedover the opening of each humidity control chamber 199 into the uppercell 129 ¹ for purposes of allowing transpiration between the humiditycontrol chamber 199 and the upper cell 129 ¹ without introducingextraneous analyte A into the upper cell 129 ¹ or allowing analyte A toescape from the upper cell 129 ¹ undetected. The selectively permeablefilm 193 can be sealingly held in position within each humidity controlchamber 199 by an o-ring 194, washer 195, inset ring 196 and lockingring 197 as shown in FIGS. 5A ¹ and 5B¹.

Use

The mounting plates 120 are removed from the retention chamber 129 byactivating the actuator 130 to lower the actuator shaft 131 into aremoval position (not shown) where the o-ring seals 180 within the gap160 no longer contact the upper section 111 of the housing 110, andsliding the mounting plates 120 out through an open side (not numbered)of the lower section 112 of the housing 110.

The upper mounting plate 121 is then separated from the lower mountingplate 122, and a sample of the film F to be tested placed atop the lowermounting plate 122 over the test chamber 129 so as to fully engage theentire periphery of the o-ring 125 encircling the test chamber 129.

The upper mounting plate 121 is then placed back atop the lower mountingplate 122 and secured to the lower mounting plate 122 so as to sealinglyclamp the film F between the plates 121 and 122, thereby sealinglyseparating the testing chamber 129 into an upper cell 129 ¹ and a lowercell 129 ² with a known area of the film F exposed to both cells 129 ¹and 129 ². The “loaded” mounting plates 120 are then slid back into theretention chamber 119.

Referring to FIGS. 4A, 4A¹, 4A² and 4A³, the actuator 130 is activatedto move the loaded mounting plates 120 into an “open” position whereinthe larger diameter o-rings 181 w, 182 w, 183 w and 198 w located withinthe gap 160 sealingly engage the lower surface 111 i of the uppersection 111 of the housing 110 while the smaller diameter o-rings 181 vand 182 v within the gap 160 do not. With the mounting plates 120 in the“open” position, the upper cell 129 ¹ is flushed with an inert gas toremove any target analyte A from the upper cell 129 ¹ by placing theinlet channel 171 a in the upper section 111 of the housing 110 in fluidcommunication with a pressurized source of inert gas 21 and allowing theinert gas to flow sequentially through the inlet channel 171 a in theupper section 111 of the housing 110, through that portion of the gap160 surrounded by the larger diameter o-ring 181 w, through the inletchannel 171 b in the upper mounting plate 121, through the upper cell129 ¹, through the outlet channel 172 b in the upper mounting plate 121,through that portion of the gap 160 surrounded by the larger diametero-ring 182 w, and out from the measurement unit 100 through the outletchannel 172 a in the upper section 111 of the housing 110.

Referring to FIGS. 4B, 4B¹, 4B² and 4B³, after flushing, the actuator130 is activated to move the loaded mounting plates 120 into a “closed”position wherein both the larger diameter o-rings 181 w, 182 w, 183 wand 198 w and smaller diameter o-rings 181 v and 182 v within the gap160 sealingly engage the lower surface 111 i of the upper section 111 ofthe housing 110 so as to seal-off the upper cell 129 ¹ from thesurrounding environment.

Referring to FIG. 4A ³, movement of the loaded mounting plates 120 intothe “closed” position also causes the pin 121 n on the upper mountingplate 121 to engage the stem 142 on the valve 140 within the passageway173 a in the upper section 111 of the housing 110 so as to open thepassageway 173 a and thereby place the analyte sensor 200 in fluidcommunication with the upper cell 129 ¹.

With the mounting plates 120 in the “closed” position, the lower cell129 ² is flushed with a test gas containing a known concentration oftarget analyte A and continuously supplied with “fresh” test gasthroughout the testing period to ensure that the concentration of targetanalyte A within the lower cell 129 ¹ remains constant. Test gas isintroduced into the lower cell 129 ² by placing the inlet channel 151 ain the upper section 111 of the housing 110 in fluid communication witha pressurized source of test gas 22 and allowing the test gas to flowsequentially through the inlet channel 151 a in the upper section 111 ofthe housing 110, through that portion of the gap 160 surrounded by thelarger diameter o-ring 151 w, through the inlet channel 151 b in theupper mounting plate 121, through the inlet channel 151 c in the lowermounting plate 122, through the lower cell 129 ², through the outletchannel 152 c in the lower mounting plate 122, through the outletchannel 152 b in the upper mounting plate 121, through that portion ofthe gap 160 surrounded by the larger diameter o-ring 152 w, and out fromthe measurement unit 100 through the outlet channel 152 a in the uppersection 111 of the housing 110.

Target analyte A will permeate through the film F as the analyte A seeksto diffuse through the film F from a region of higher concentration(i.e., the lower cell 129 ²) to a region of lower concentration (i.e.,the upper cell 129 ¹). Since test gas continuously flows through thelower cell 129 ² the concentration of target analyte A in the region ofhigher concentration remains constant throughout the relevant testperiod. Similarly, since the analyte sensor 200 consumes target analyteA within the upper cell 129 ¹ faster that the target analyte A permeatesthrough the film F, the concentration of target analyte A in the regionof lower concentration also remains constant at essentially zerothroughout the relevant test period.

Eventually, the system will reach a steady state condition where therate at which analyte A is detected in the upper cell 129 ¹ by theanalyte sensor 200 and reported by the central processing unit 50remains constant. This steady state rate equates directly to thepermeation rate for the film F for the “exposed” area of the film.

EXAMPLES Example 1

A 1.0 mil thick polyethylene terephthalate mylar film is placed betweenthe mounting plates of the permeation testing system depicted in FIGS.1-7 so as to provide a 50 cm² area of the film exposed to both the upperand lower cells. Permeation testing is conducted in accordance with ASTMD3985 employing the following testing parameters:

Gas In Upper Cell: Type: 100% N₂ RH:  10% Gas In Lower Cell: Type: 100%O₂ RH:  10% Testing Chamber Temp: 23° C. Barometer: 742.3 mmHg

Oxygen within the upper cell is continuously sensed with ahigh-sensitivity standard electrochemical oxygen sensor covered with aporous membrane. Utilizing a reporting cycle of five (5) minutes, thetransmission rate of oxygen through the film (O2TR) is calculated fromthe amperes sensed by the sensor each reporting cycle utilizing EQUATIONA. The O2TR calculated for each reporting cycle throughout the testingperiod is depicted in FIG. 8 and set forth in Table One below. The O2TRfor the film, reported after fifty (50) reporting cycles (4 hours and 10minutes) is 60.975 cm³/(m²)(day).O2TR=Amperes/(Area)(k ₁)(k ₂)(k ₃)  (EQUATION A)Wherein:

-   O2TR=Transmission Rate of Oxygen (cm³/(m²)(sec))-   Amperes=Amperes generated at the sensor (coulombs/second)-   Area=Exposed area of the film (m²)-   k₁=Molecules of Oxygen per cm³ at Standard Temperature and Pressure    (2.6876*10¹⁹ molecules/cm³)-   k₂=Electrons involved in covalent bonding @ the sensor per molecule    of Oxygen (4 e⁻/molecule)-   k₃=Coulombs generated per electron (1.6*10⁻¹⁹ coulombs/e-)

TABLE ONE Time O2TR (hrs:min) cm³/(m²)(day)   5 0.1   10 5.078   1515.105   20 25.023   25 33.235   30 39.666   35 47.96   40 51.218   4553.614   50 55.399   55 56.72 1:00 57.732 1:05 58.499 1:10 59.073 1:1559.491 1:20 59.844 1:25 60.086 1:30 60.254 1:35 60.397 1:40 60.51 1:4560.592 1:50 60.67 1:55 60.715 2:00 60.769 2:05 60.785 2:10 60.807 2:1560.84 2:20 60.857 2:25 60.843 2:30 60.858 2:35 60.858 2:40 60.896 2:4560.9 2:50 60.935 2:55 60.952 3:00 60.957 3:05 60.973 3:10 60.97 3:1560.966 3:20 60.954 3:25 60.959 3:30 60.948 3:35 60.98 3:40 60.984 3:4560.978 3:50 60.974 3:55 60.973 4:00 60.984 4:05 60.968 4:10 60.975

1. A valve system, comprising: (a) first and second longitudinallyfacing members defining a gap therebetween in fluid communication withtransversely offset first and second orifices through the members,wherein one of the members is longitudinally repositionable relative tothe other member for adjusting the longitudinal height of the gap, (b) aprimary biasing means longitudinally biasing the members away from oneanother, (c) an elastic element positioned within the gap between thefirst and second orifices, (d) a repositioning means for longitudinallyrepositioning the repositionable member towards the other member againstthe bias of the primary biasing means as between (i) a first positionwherein the elastic element does not seal the gap so as to allow fluidflow from the first orifice to the second orifice through the gap, and(ii) a second position wherein the elastic element is compressed betweenthe members and seals the gap so as to prevent fluid flow from the firstorifice to the second orifice through the gap.
 2. The valve system ofclaim 1 wherein the first orifice extends through the first member andthe second orifice extends through the second member.
 3. The valvesystem of claim 1 wherein the primary biasing means is a larger-diameterelastic O-ring positioned within the gap and encompassing both the firstand second orifices.
 4. The valve system of claim 3 wherein the elasticelement is a smaller-diameter elastic O-ring surrounding only one of thefirst or second orifice.
 5. The valve system of claim 4 wherein thelongitudinal height of the larger-diameter elastic O-ring is greaterthan the longitudinal height of the smaller-diameter elastic O-ring. 6.The valve system of claim 1 wherein the repositioning means is anadjustable-strength biasing means for longitudinally biasing therepositionable member towards the other member against the bias of theprimary biasing means between (i) a first biasing strength sufficient toachieve the first position, and (ii) a second biasing strengthsufficient to achieve the second position.
 7. The valve system of claim6 wherein the adjustable-strength biasing means is a pneumatic piston.8. The valve system of claim 6 wherein the adjustable-strength biasingmeans is a hydraulic piston.
 9. A bidirectional valve system,comprising: (a) first and second longitudinally facing members defininga gap therebetween in fluid communication with a first inlet and a firstoutlet orifice through one member and a second inlet and a second outletorifice through the other member, wherein (i) the inlet orifices aretransversely offset, (ii) the outlet orifices are transversely offset,and (iii) one of the members is longitudinally repositionable relativeto the other member for adjusting the longitudinal height of the gap,(b) an inlet larger-diameter elastic O-ring positioned within the gapand encompassing both the first and second inlet orifices, (c) an inletsmaller-diameter elastic O-ring positioned within the gap andsurrounding only one of the first or second inlet orifices, (d) anoutlet larger-diameter elastic O-ring positioned within the gap andencompassing both the first and second outlet orifices, (e) an outletsmaller-diameter elastic O-ring positioned within the gap andsurrounding only one of the first or second outlet orifices, (f) arepositioning means for longitudinally repositioning the repositionablemember towards the other member against the bias of the larger-diameterelastic O-rings as between (i) a first position wherein thelarger-diameter O-rings are compressed between the members and seal thegap so as to prevent fluid flow through the gap from the inlet orificesto the outlet orifices without compressing the smaller-diameter O-ringsbetween the members so as to allow fluid flow from the first inletorifice to the second inlet orifice through the gap and from the firstoutlet orifice to the second outlet orifice through the gap, and (ii) asecond position wherein both larger-diameter O-rings are compressedbetween the members and seal the gap so as to prevent fluid flow throughthe gap from the inlet orifices to the outlet orifices, the inletsmaller-diameter O-ring is compressed between the members so as toprevent fluid flow from the first inlet orifice to the second inletorifice through the gap, and the inlet smaller-diameter O-ring iscompressed between the members so as to prevent fluid flow from thefirst outlet orifice to the second outlet orifice through the gap. 10.The bidirectional valve system of claim 9 wherein the longitudinalheight of the larger-diameter elastic O-rings is greater than thelongitudinal height of the smaller-diameter elastic O-rings.
 11. Thebidirectional valve system of claim 9 wherein the repositioning means isan adjustable-strength biasing means for longitudinally biasing therepositionable member towards the other member against the bias of thelarger-diameter elastic O-rings between (i) a first biasing strengthsufficient to achieve the first position, and (ii) a second biasingstrength sufficient to achieve the second position.
 12. The valve systemof claim 11 wherein the adjustable-strength biasing means is a pneumaticpiston.
 13. The valve system of claim 11 wherein the adjustable-strengthbiasing means is a hydraulic piston.